New information is surfacing about a Japanese submarine military exercise in the South China Sea. The Maritime Self-Defense Force (MSDF) said in a rare statement on Monday that one submarine and three other vessels performed aggressive maneuvers to deter China’s militarization of the region.

“Japan has been performing submarine exercises in the South China Sea since 15 years ago. We did so last year and the year before that,” Prime Minister Shinzo Abe said on a TV program on Monday. “The purpose of the Self-Defense Force drills is to improve their skill. It is not intended for specific countries.”

According to the Nikkei Asian Review, this is the first public announcement that the MSDF revealed military exercises by a submarine in the region. Last Thursday, the Hiroshima-based submarine Kuroshio joined helicopter carrier Kaga and two other missile destroyers for maneuvers.

During the exercise, destroyers worked with helicopters to hunt for the submarine using sonars, while the Kuroshio pursued the carrier as it lurked beneath the waters. What is notable, however, is that the exercises took place within China’s self-declared maritime claim known as the Nine-Dash Line, which includes most of the South China Sea.

“It’s part of a strategic message that Japan would like to send to China and the countries in the region,” said Narushige Michishita, a professor specializing in international security at the National Graduate Institute for Policy Studies in Tokyo. “It’s a demonstration of Japan’s will to maintain a balance of power.” Michishita called it “very significant” that Tokyo would even send anti-submarine warfare capability because China regularly operates nuclear-powered submarines in the area.

After the exercise, the Japanese sub made a port call to Cam Ranh Bay Monday to visit their Vietnamese friends. The move was seen as a key indication as Vietnam also opposes China’s militarization in the nearby waters. The exercise concluded just after the British and French conducted freedom of navigation tours in the South China Sea, a move that the US Navy carries out on a regular basis.

Chinese Foreign Ministry spokesman Geng Shuang, was questioned about the Japanese exercise at a recent press briefing, did not directly criticize Tokyo but said countries outside the South China Sea region “should act cautiously and avoid harming regional peace and stability,” said The Wall Street Journal.

Geng said the environment in the South China Sea was slightly improving and China was committed to working with Southeast Asian countries to resolve disputed economic zones.

However, the Japanese exercise could complicate the recent improvement in relations between Tokyo and Beijing, which developed after the Trump administration slapped both countries with tariffs.

Meanwhile, the fate of the world seems to be on a rocky path, and the reason why Japan is preparing for war in the South China Sea may be simply because it views Sino-US relations as nearing a point of no return as a result of the escalation from the trade ongoing war.